With the current focus of concern about carbon emissions from transport, we tend to overlook the possible impact of other kinds of emissions.  Relevant to this, the UK Committee on the Medical Effects of Air Pollutants (COMEAP) has recently published a report Long-term Exposure to Air Pollution: Effect on Mortality.  The pollutant of main concern is fine particles designated PM_2.5 – particles of less than 2.5 micron diameter, mostly carbon, much of which derives from vehicle exhausts.  The aim of the Committee has been to quantify the relationship between an increase in ambient particulate concentration and the resulting increase in mortality, based on a detailed technical analysis of the available research findings.

To see the impact of this analysis, one has to go back a couple of years to a document titled An Economic Analysis to inform the Air Quality Strategy which incorporates an earlier but very similar COMEAP relationship. One approach to presenting the consequences of pollution is to estimate the impact that this has on life expectancy, both for current levels of particulates and for those expected as the result of measures to reduce emissions. Life expectancy is reduced on account of air pollution by about 7 months at present, falling to about 5 months as a result of planned reduction measures.

5-7 months' reduction in life expectancy, from what it would otherwise be, might sound quite a lot.  On the other hand, overall life expectancy is increasing by leaps and bounds – by about 3 months for each year that passes.  So cutting air pollution to improve life expectancy by a couple of months (7 minus 5) would be hard to detect against this background of pretty spectacular improvement.  My conclusion: the harmful effects on health of vehicle particulate emissions, while not trivial, equally are not decisive as a driver of policy – unlike carbon.